[Linux] 如何使用Valgrind memcheck工具进行C/C++的内存泄漏检测

梦里梦外; 2022-04-11 06:07 222阅读 0赞

转自  
\[url\]http://www.oschina.net/translate/valgrind-memcheck\[/url\]  
  
系统编程中一个重要的方面就是有效地处理与内存相关的问题。你的工作越接近系统，你就需要面对越多的内存问题。有时这些问题非常琐碎，而更多时候它会演变成一个调试内存问题的恶梦。所以，在实践中会用到很多工具来调试内存问题。  
在本文中，我们将讨论最流行的开源内存管理框架 VALGRIND。  
  
许多有用的工具被作为标准而提供。  
Memcheck是一个内存错误检测器。它有助于使你的程序，尤其是那些用C和C++写的程序，更加准确。  
Cachegrind是一个缓存和分支预测分析器。它有助于使你的程序运行更快。  
Callgrind是一个调用图缓存生成分析器。它与Cachegrind的功能有重叠，但也收集 Cachegrind不收集的一些信息。  
Helgrind是一个线程错误检测器。它有助于使你的多线程程序更加准确。  
DRD也是一个线程错误检测器。它和Helgrind相似，但使用不同的分析技术，所以可能找到不同的问题。  
Massif是一个堆分析器。它有助于使你的程序使用更少的内存。  
DHAT是另一种不同的堆分析器。它有助于理解块的生命期、块的使用和布局的低效等问题。  
SGcheck是一个实验工具，用来检测堆和全局数组的溢出。它的功能和Memcheck互补：SGcheck找到Memcheck无法找到的问题，反之亦然。  
BBV是个实验性质的SimPoint基本块矢量生成器。它对于进行计算机架构的研究和开发很有用处。  
也有一些对大多数用户没有用的小工具：Lackey是演示仪器基础的示例工具；Nulgrind是一个最小化的Valgrind工具，不做分析或者操作，仅用于测试目的。  
在这篇文章我们将关注“memcheck”工具。  
  
  
\[align=center\]\[b\]使用 Valgrind Memcheck\[/b\]\[/align\]  
  
memcheck工具的使用方式如下:  
\[quote\]valgrind --tool=memcheck ./a.out\[/quote\]  
从上面的命令可以清楚的看到, 主要的命令是valgrind，而我们想使用的工具是通过'-tool'选项来指定的. 上面的‘a.out’指的是我们想使用memcheck运行的可执行文件.  
该工具可以检测下列与内存相关的问题 :  
未释放内存的使用  
对释放后内存的读/写  
对已分配内存块尾部的读/写  
内存泄露  
不匹配的使用malloc/new/new\[\] 和 free/delete/delete\[\]  
重复释放内存  
注意: 上面列出的并不很全面，但却包含了能被该工具检测到的很多普遍的问题.  
让我们一个一个地对上面的场景进行讨论:  
注意: 下面讨论的所有测试代码都应该使用gcc并且加上-g选项(用来在memcheck的输出中生成行号)进行编译. 就想我们之前讨论过的 C程序被编译成可执行文件, 它需要经历四个不同的阶段.  
  
  
\[b\]1. 使用未初始化的内存\[/b\]  
Code :

#include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       
        char *p;
    
        char c = *p;
    
        printf("\n [%c]\n",c);
    
        return 0;
    }

在上面的代码中，我们尝试使用未初始化的指针 ‘p’.  
让我们运行Memcheck来看下结果.  
\[quote\]$ valgrind --tool=memcheck ./val  
==2862== Memcheck, a memory error detector  
==2862== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.  
==2862== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info  
==2862== Command: ./val  
==2862==  
==2862== Use of uninitialised value of size 8  
==2862== at 0x400530: main (valgrind.c:8)  
==2862==  
  
\[\#\]  
==2862==  
==2862== HEAP SUMMARY:  
==2862== in use at exit: 0 bytes in 0 blocks  
==2862== total heap usage: 0 allocs, 0 frees, 0 bytes allocated  
==2862==  
==2862== All heap blocks were freed -- no leaks are possible  
==2862==  
==2862== For counts of detected and suppressed errors, rerun with: -v  
==2862== Use --track-origins=yes to see where uninitialized values come from  
==2862== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)\[/quote\]  
从上面的输出可以看到,Valgrind检测到了未初始化的变量，然后给出了警告(上面加粗的几行(译者注：貌似上面没有加粗的)).  
  
  
\[b\]2. 在内存被释放后进行读/写\[/b\]  
Code :

#include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       
        char *p = malloc(1);
        *p = 'a';
    
        char c = *p;
    
        printf("\n [%c]\n",c);
    
        free(p);
        c = *p;
        return 0;
    }

上面的代码中，我们有一个释放了内存的指针 ‘p’ 然后我们又尝试利用指针获取值.  
让我们运行memcheck来看一下Valgrind对这种情况是如何反应的.  
\[quote\]$ valgrind --tool=memcheck ./val  
==2849== Memcheck, a memory error detector  
==2849== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.  
==2849== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info  
==2849== Command: ./val  
==2849==  
  
\[a\]  
==2849== Invalid read of size 1  
==2849== at 0x400603: main (valgrind.c:30)  
==2849== Address 0x51b0040 is 0 bytes inside a block of size 1 free'd  
==2849== at 0x4C270BD: free (vg\_replace\_malloc.c:366)  
==2849== by 0x4005FE: main (valgrind.c:29)  
==2849==  
==2849==  
==2849== HEAP SUMMARY:  
==2849== in use at exit: 0 bytes in 0 blocks  
==2849== total heap usage: 1 allocs, 1 frees, 1 bytes allocated  
==2849==  
==2849== All heap blocks were freed -- no leaks are possible  
==2849==  
==2849== For counts of detected and suppressed errors, rerun with: -v  
==2849== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)\[/quote\]  
从上面的输出内容可以看到，Valgrind检测到了无效的读取操作然后输出了警告 ‘Invalid read of size 1′.  
另注,使用gdb来调试c程序.  
  
  
\[b\]3. 从已分配内存块的尾部进行读/写\[/b\]  
Code :

#include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       
        char *p = malloc(1);
        *p = 'a';
    
        char c = *(p+1);
    
        printf("\n [%c]\n",c);
    
        free(p);
        return 0;
    }

在上面的代码中，我们已经为‘p’分配了一个字节的内存,但我们在将值读取到 ‘c’中的时候使用的是地址p+1.  
现在我们使用Valgrind运行上面的代码 :  
\[quote\]$ valgrind --tool=memcheck ./val  
==2835== Memcheck, a memory error detector  
==2835== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.  
==2835== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info  
==2835== Command: ./val  
==2835==  
==2835== Invalid read of size 1  
==2835== at 0x4005D9: main (valgrind.c:25)  
==2835== Address 0x51b0041 is 0 bytes after a block of size 1 alloc'd  
==2835== at 0x4C274A8: malloc (vg\_replace\_malloc.c:236)  
==2835== by 0x4005C5: main (valgrind.c:22)  
==2835==  
  
\[\]  
==2835==  
==2835== HEAP SUMMARY:  
==2835== in use at exit: 0 bytes in 0 blocks  
==2835== total heap usage: 1 allocs, 1 frees, 1 bytes allocated  
==2835==  
==2835== All heap blocks were freed -- no leaks are possible  
==2835==  
==2835== For counts of detected and suppressed errors, rerun with: -v  
==2835== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)\[/quote\]  
同样，该工具在这种情况下也检测到了无效的读取操作.  
  
\[b\]4. 内存泄露\[/b\]  
Code:

#include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       
        char *p = malloc(1);
        *p = 'a';
    
        char c = *p;
    
        printf("\n [%c]\n",c);
    
        return 0;
    }

在这次的代码中, 我们申请了一个字节但是没有将它释放.现在让我们运行Valgrind看看会发生什么：  
\[quote\]$ valgrind --tool=memcheck --leak-check=full ./val  
==2888== Memcheck, a memory error detector  
==2888== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.  
==2888== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info  
==2888== Command: ./val  
==2888==  
  
\[a\]  
==2888==  
==2888== HEAP SUMMARY:  
==2888== in use at exit: 1 bytes in 1 blocks  
==2888== total heap usage: 1 allocs, 0 frees, 1 bytes allocated  
==2888==  
==2888== 1 bytes in 1 blocks are definitely lost in loss record 1 of 1  
==2888== at 0x4C274A8: malloc (vg\_replace\_malloc.c:236)  
==2888== by 0x400575: main (valgrind.c:6)  
==2888==  
==2888== LEAK SUMMARY:  
==2888== definitely lost: 1 bytes in 1 blocks  
==2888== indirectly lost: 0 bytes in 0 blocks  
==2888== possibly lost: 0 bytes in 0 blocks  
==2888== still reachable: 0 bytes in 0 blocks  
==2888== suppressed: 0 bytes in 0 blocks  
==2888==  
==2888== For counts of detected and suppressed errors, rerun with: -v  
==2888== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)\[/quote\]  
输出行(上面加粗的部分)显示，该工具能够检测到内存的泄露.  
注意: 在这里我们增加了一个选项‘–leak-check=full’来得到内存泄露的详细细节.  
ToB蓝波湾  
ToB蓝波湾  
翻译于 3年前  
1人顶  
顶 翻译的不错哦!  
5. 不匹配地使用malloc/new/new\[\] 和 free/delete/delete\[\]  
  
Code:

#include <stdio.h>
    #include <stdlib.h>
    #include<iostream>
    
    int main(void)
    {
       
        char *p = (char*)malloc(1);
        *p = 'a';
    
        char c = *p;
    
        printf("\n [%c]\n",c);
        delete p;
        return 0;
    }

上面的代码中，我们使用了malloc()来分配内存，但是使用了delete操作符来删除内存.  
注意 : 使用g++来编译上面的代码，因为delete操作符是在C++中引进的，而要编译C++需要使用g++.  
让我们运行来看一下 :  
\[quote\]$ valgrind --tool=memcheck --leak-check=full ./val  
==2972== Memcheck, a memory error detector  
==2972== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.  
==2972== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info  
==2972== Command: ./val  
==2972==  
  
\[a\]  
==2972== Mismatched free() / delete / delete \[\]  
==2972== at 0x4C26DCF: operator delete(void\*) (vg\_replace\_malloc.c:387)  
==2972== by 0x40080B: main (valgrind.c:13)  
==2972== Address 0x595e040 is 0 bytes inside a block of size 1 alloc'd  
==2972== at 0x4C274A8: malloc (vg\_replace\_malloc.c:236)  
==2972== by 0x4007D5: main (valgrind.c:7)  
==2972==  
==2972==  
==2972== HEAP SUMMARY:  
==2972== in use at exit: 0 bytes in 0 blocks  
==2972== total heap usage: 1 allocs, 1 frees, 1 bytes allocated  
==2972==  
==2972== All heap blocks were freed -- no leaks are possible  
==2972==  
==2972== For counts of detected and suppressed errors, rerun with: -v  
==2972== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)\[/quote\]  
从上面的输出可以看到 (加粗的行), Valgrind清楚的说明了‘不匹配的使用了free() / delete / delete \[\]‘  
你可以尝试在测试代码中使用'new'和'free'进行组合来看看Valgrind给出的结果是什么.  
ToB蓝波湾  
ToB蓝波湾  
翻译于 3年前  
3人顶  
顶 翻译的不错哦!  
6. 两次释放内存  
  
Code :

#include <stdio.h>
    #include <stdlib.h>
    
    int main(void)
    {
       
        char *p = (char*)malloc(1);
        *p = 'a';
    
        char c = *p;
        printf("\n [%c]\n",c);
        free(p);
        free(p);
        return 0;
    }

在上面的代码中, 我们两次释放了'p'指向的内存. 现在让我们运行memcheck :

$ valgrind --tool=memcheck --leak-check=full ./val
    ==3167== Memcheck, a memory error detector
    ==3167== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
    ==3167== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
    ==3167== Command: ./val
    ==3167==
    
     [a]
    ==3167== Invalid free() / delete / delete[]
    ==3167==    at 0x4C270BD: free (vg_replace_malloc.c:366)
    ==3167==    by 0x40060A: main (valgrind.c:12)
    ==3167==  Address 0x51b0040 is 0 bytes inside a block of size 1 free'd
    ==3167==    at 0x4C270BD: free (vg_replace_malloc.c:366)
    ==3167==    by 0x4005FE: main (valgrind.c:11)
    ==3167==
    ==3167==
    ==3167== HEAP SUMMARY:
    ==3167==     in use at exit: 0 bytes in 0 blocks
    ==3167==   total heap usage: 1 allocs, 2 frees, 1 bytes allocated
    ==3167==
    ==3167== All heap blocks were freed -- no leaks are possible
    ==3167==
    ==3167== For counts of detected and suppressed errors, rerun with: -v
    ==3167== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)

从上面的输出可以看到(加粗的行), 该功能检测到我们对同一个指针调用了两次释放内存操作.  
在本文中，我们把注意力放在了内存管理框架Valgrind，然后使用memcheck(Valgrind框架提供的)工具来了解它是如何降低需要经常操作内存的程序员的负担的. 该工具能够检测到很多手动检测不到的与内存相关的问题